1. Field of Inventions
Embodiments of the present inventions generally relate to compositions containing polyethylene.
2. Description of Related Art
Although bimodal polyethylene compositions have numerous advantages, and have solved various problems in the art, an ongoing need exists for further improvements, particularly in films and polyethylene compositions used to make films. Some of the properties used to characterize films are Elmendorf Tear (MD and TD) values, which are properties based on the procedures set forth in ASTM D 1922. The MD Elmendorf Tear value refers to tear resistance properties in the “machine direction” while the TD Elmendorf Tear value refers to tear resistance properties in the “transverse direction.” It is generally desirable to balance the two values. A film that has a highly unbalanced TD/MD ratio, e.g., over 10, is often found to be splitty, and to experience zippering when subjected to tear. At least some of the compositions described herein have improved “tear balance,” a term that refers to the TD/MD ratio of a film made from that particular composition. As discussed herein, a composition with a better tear balance is one that can be formed into a film with a lower TD/MD ratio (closer to unity or 1) than a composition with a worse tear balance, such that a film made of the latter composition has a higher, and less desirable, TD/MD ratio.
Certain patents that refer to polyethylene compositions, and methods for making polyethylene, include the following: U.S. Pat. Nos. 4,336,352; 5,091,228; 5,110,685; 5,208,309; 5,274,056; 5,635,262; 5,338,589; 5,344,884; 5,378,764; 5,494,965; 5,739,225; 5,795,941; 6,090,893; 6,340,730; 6,359,072; 6,388,017; 6,388,115; 6,403,717; 6,420,580; 6,441,096; 6,476,166; 6,534,604; 6,562,905; 6,605,675; 6,608,149; and WO 97/47682 and WO 94/22948. Other patents and publications are listed on the cover page of the patent.